With the discovery of hydrocarbon producing fields located at ever increasing water depths, the use of rigid structures fixed on the sea bed, intended for installation of production equipment, has become more complex by the day. In some cases, owing to the particular conditions of the region where the hydrocarbon producing field is located, their use has become unviable.
In more recent times, floating structures represent an alternative that is used more and more frequently for the installation of production equipment, as they normally offer a lower-cost option compared to fixed structures.
Petroleum production in deep water makes extensive use of riser pipes, also known as risers. This tubing, which may be flexible or rigid, collects the oil produced by the subsea well, and conveys it to a floating unit, and then to tankers, or directly to onshore installations.
The installation and dismantling of the risers in the structure of the floating unit are known as pull-in and pull-out operations. A pull-in/pull-out cable, connected to a submerged supporting system that supports a riser, suspends an assembly of the riser and supporting system until the connector of the latter engages in a support of the stationary production unit (SPU) and can be fixed and secured manually.
The company SBM has developed a system of wedges for fixing and securing the connectors of the supporting systems, especially for supporting systems of the I-tube type, illustrated in FIG. 1.
The fixing and securing of the connector of the supporting system is carried out with the assistance of divers, since these operations are not fully automated.
However, since the method for installing flexible risers conventionally employed in the prior art requires the use of divers and the mobilization of support ships, this method is subject to the sea conditions for a certain period of time. This dependence on the weather conditions may generate unexpected delays in projects, owing to the long waiting periods for good diving conditions.
In an attempt to solve this problem, some techniques for fixing and securing riser supporting systems may be found in the prior art. Some of them are described briefly below.
U.S. Pat. No. 7,373,986B2 discloses a connector for risers comprising a double-click securing system. In the pull-in operation, an enlargement or joint positioned in the upper portion of a riser enters a pocket fixed to the structure of a platform. A joint or enlargement comprises supporting surfaces comprising cams that engage in recesses of the pocket. The pockets are arranged side by side and the engagement of the cams is guided by guides that move the cams angularly until they are located on the recesses. Then the riser is lowered until the cams engage in the recesses.
U.S. Pat. No. 5,947,642A describes a device for coupling flexible risers comprising a tensioner provided with a projection and an angularly moveable retainer for securing the projection automatically when the tensioner is raised into a cylindrical pocket.
U.S. Pat. No. 7,967,070B2 also discloses a connector comprising a funnel/guide assembly to be coupled to an underwater structure, wherein the funnel/guide assembly receives a shaft. The shaft is coupled to a tensioner. A securing assembly is coupled to the funnel/guide assembly, wherein the securing assembly comprises a securing device. Retainers move into and out of the funnel/guide assembly, wherein the retainers are inserted into recesses of the shaft for securing the axial movement of the shaft relative to the funnel/guide assembly. The connector is installed and secured using a remotely operated vehicle (ROV).
Although the prior art comprises various devices and systems for securing supporting systems or tensioners of risers, many of them are complex and/or require precise adjustments for said securing. Moreover, many will need at least the assistance of a ROV, which may make the pull-in/pull-out operation unviable in extreme sea conditions.
As will be explained in detail hereunder, the present invention aims to provides a simple, low-cost alternative for automatic installation and securing of supporting systems.